In producing silver halide photographic light-sensitive materials, it is well known to form silver halide in a binder (protective colloid) such as gelatin and coat the resulting emulsion on a support. However, silver halide and the binder are conventionally used in a proportion of about 1:1 in terms of the ratio of silver halide (calculated as silver) to binder. This applies not only to "surface latent image type emulsions" (negative-working emulsions) which form latent images predominantly on the surface of the silver halide grains but also to "internal latent image type emulsions" which form latent images predominantly inside the silver halide grains and which are used as direct positive emulsions for forming direct positive images as well.
Specific examples of the binder-to-silver ratio in light-sensitive materials having internal latent image type direct positive emulsion layer are described below. In Example 9 described in U.S. Pat. No. 3,923,513, the ratios are 1.2 (red-sensitive layer), 0.9 (green-sensitive layer), and 1.0 (blue-sensitive layer) and, in Example 11, the ratios are 0.8 (red-sensitive layer), 0.83 (green-sensitive layer), and 0.67 (blue-sensitive layer).
In U.S. Pat. No. 4,356,250 which discloses incorporating zinc oxide in an interlayer provided between a green-sensitive layer and a blue-sensitive layer, the ratio is 1.0 (in all of red-, green- and blue-sensitive layers) and, in Japanese Patent Application (OPI) No. 17435/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") which discloses incorporating a solid pigment such as titanium white in an interlayer provided between an internal latent image type emulsion layer and a layer containing a dye providing compound, the ratio is 0.79. Further, in U.S. Pat. No. 4,332,885 which discloses providing a plurality of internal latent image type emulsions having the same color sensitivity, the ratio is 1.0 to 1.17.
Of the photographic light-sensitive materials having internal latent image type direct positive silver halide emulsion layers, those which contain at least one silver halide emulsion layer unit comprising at least two internal latent image type direct positive silver halide emulsion layers with substantially the same color sensitivity and different light sensitivities as disclosed in above-mentioned U.S. Pat. No. 4,332,885 have the advantage, in comparison with those in which at least two emulsions are mixed in place of providing a plurality of layers, in that:
(1) higher sensitivity can be attained since optional amounts of sensitizers, nucleating agents, etc., to be added to respective silver halide emulsion layers can be selected;
(2) the problem of "processing temperature dependence", i.e., that the image density varies depending upon the processing temperature, can be solved to some extent; and
(3) gradation can be easily controlled.
Therefore, photographic light-sensitive materials of this type are excellent for forming photographs with high image quality.
In addition, photographic light-sensitive materials of the type which have a solid pigment-containing layer contiguous to an internal latent image type direct positive silver halide emulsion layer as disclosed in Japanese Patent Application (OPI) No. 17435/83 are also excellent for forming photographs with high image quality, because they prevent inhibition of silver development and, therefore, show enhanced sensitivity.
However, light-sensitive materials of these types have a common technical problem of poor storage stability, the reason therefore not being well understood. Thus, solution of this problem is of importance for providing photographs having better image quality.